Current mirrors are extensively used in integrated circuit (IC) devices. Their main function is in so-called turnaround circuits where a current sink is turned into a current source or vice versa. Such an action shifts the circuit voltage level so that a substantial potential level shift can be achieved without losing the d-c reference level.
Reference is made to U.S. Pat. No. 4,528,496 which issued July 9, 1985. This patent, by Toyojiro Naokawa and Matsuro Koterasawa, is titled CURRENT SUPPLY FOR USE IN LOW VOLTAGE IC DEVICES, and assigned to the assignee of the present application. The patent is directed to a current mirror that operates at low supply levels and it teaches the basic current mirror configurations. The teaching in the patent is incorporated herein by reference.
In certain circuit applications, particularly those in which a capacitive load is being driven, it can be advantageous to speed up the circuit turn on and also to provide a current overshoot for a short period of time after turn on to increase the slew rate. One such application is the driving of the switching devices in a buck-type switching regulator power supply. Another is the base discharge of a grounded emitter power switching transistor.